Computer systems are typically comprised of a variety of different components or devices that operate together to form the resultant system. Some of the devices are supplied with the computer system initially, such as the central processing unit, and some devices can be installed into the computer system after the initial configuration of the system. The devices of the computer system are generally coupled together via interconnects which may be of several types, such as a serial bus.
Serial buses are well known in the art. A recently developed serial bus standard is the IEEE 1394 serial bus standard, disclosed in the ISO/IEC 13213 (ANSI/IEEE 1212) CSR Architecture Specification and the IEEE 1394-1995 Serial Bus Specification, the teachings of which are herein incorporated by this reference. A typical serial bus having an IEEE 1394 standard architecture is comprised of a multiplicity of nodes that are interconnected via point-to-point links, such as cables, that each connects a single node of the serial bus to another node of the serial bus. Each node is an addressable entity that can be reset and identified. Nodes are associated with respective components of the computer system and serve as interfaces between the components and communication links. Each node has a configuration ROM (CROM), the registers of which can be accessed by software residing within the computer system. The IEEE 1394 standard sets forth a general CROM format which comprises several fields. One field in particular is the unit directory. The unit directory contains information representing the functionality of units within the node, particularly the unit's software version number and its location within the node. Generally, the information in the configuration ROM is treated as static. However, U.S. Pat. No. 6,643,714 entitled “Modification and Use of Configuration Memory Used During Operation of a Serial Bus” provides a technique for dynamically changing the configuration ROM, the teachings of which are herein incorporated by this reference. This patent describes a technique of creating multiple unit directories for multiple device representation.
Device drivers are well known in the art. When a user installs a new device on to a computer system, a device driver is loaded for communication with the device. A device driver is software within an operating system that controls a device. A virtual device driver is a special type of device driver that has full access to the operating system kernel and can communicate directly to a physical port but was loaded without a hardware device being detected or enumerated by the system. A virtual device driver manipulates kernel mode code using existing hardware resources to emulate a device that is not normally present on the computer. In connection with a 1394 serial bus, a virtual driver is given more access than a traditional device driver because it is not restricted to talking to just one particular device.
Virtual device drivers are designed to handle hardware device contention between multiple processes and to translate or buffer data transfers from a virtual machine to hardware devices. A virtual machine is a self-contained operating environment that behaves as if it were a separate computer. When two or more processes attempt to access the same device, some method of contention management must be used. A virtual device driver allows each process to act as though it has exclusive access to the device. For example, a virtual printer driver would provide the printing process with a virtual printer port, and characters written to the port would be written to a print spooler. The virtual device driver would then send the job to the printer when it becomes available. Another method would be to assign the physical device to only one process at a time, so that when a process attempts to access the device while it is in use, the virtual device driver does not pass the request to the actual hardware, and the process operates as though the hardware did not exist.
Recently, virtual device drivers have been expanded to include interprocess communication. Virtual device drivers can provide the necessary mechanisms to allow a virtual machine to see a device that may not actually exist in hardware. Virtual device drivers can also implement client-server hardware management by providing an interface to a virtual machine. Virtual device drivers also virtualize input/output to the device and translate this information into commands to be sent across a network to a hardware server.
Currently, when a device is plugged into a personal computer (PC) on a 1394 bus, the 1394 bus driver interface creates a device object. Based on the device object, the so-called plug and play (PnP) subsystem loads high level device drivers that facilitate communication between the user and the device. At this time, the PC does not emulate any device, rather the PC exposes a generic CROM on the 1394 bus. Other nodes on the bus use the CROM to detect that the PC is in fact a PC. Enumeration occurs when a node on a serial bus accesses the configuration memory of another node to see what functionality the node has. The node accessing the CROM would then load a device object and device driver according to what functionality was exposed in the configuration memory. A technique that allows device emulation on a hardware platform that runs a general purpose operating system is not currently known in the art. However, such a technique would offer significant advantages over the prior art.
A further problem with current technology is the inability of devices to communicate natively, i.e., without translations, over a serial bus. For example, streaming video between two or more PCs will typically require translations at the transmitting and receiving ends of a serial bus. A first PC may have an audio video interleave (AVI) file that it wishes to send to a second PC. AVI is currently a video standard in a “WINDOWS” brand operating system. In order to send the file, the first PC would have to convert the AVI file to network packets and then stream it over the Internet protocol (IP) network. A technique that allows devices to transmit such files over a serial bus without converting the files is not currently known in the art. However, such a technique would offer significant advantages over the prior art.